Our current work involves the formation and isolation of two-dimensional crystals of photosystem II, its imaging by low-dose electron microscopy, and image processing to determine the structure of photosystem II. Several programs developed in the Boulder Laboratory for 3D Fine Structure have been used in this work, as well as specific pieces of equipment. In particular, all digitizing of negatives has been done in the HVEM facilities, using programs developed by David Mastronarde. Analysis of antibody labeled crystals was also done using programs developed by Dr. Mastronarde (J. Cell Biol. 132, 823-833). In related work, some very large crystals were processed on the SGI computer and detailed analysis of volumes and potential masses were done using the IMOD programs developed by Jim Kremer (J. Struct. Biol. 117, 86-98). Currently, the PS II crystals are being analyzed using MRC-based programs. This has been accomplished by using the Dec 3000 computer as a terminal for the SGI in the HVEM facility, particularly for running the SPECTRA set of programs to index the transforms. In the future, some of the analysis will be done directly on the SGI, as the data sets and displays have become too large for the Dec. In addition, both David Mastronarde and Jim Kremer have provided invaluable help with respect to setting up, debugging and running programs. [unreadable]